I need help with for loops with if statements. I'm trying to get it to output [P,O,O,O,P​​,O,P,U,U,​O​,O,O,U,O​,O​,A,A,A,​P,P​,G,O,U​,U,G​,A,P,​O]. thx

volt=[18 33 31 34 15 37 10.5 48 50 38 35 39 42 33 31 1 5 9 13 11 27 35 -1 46 22 6 19 36];
[fruit_for]=Program05a(volt);
% separate scirpt below  
function[fruit_for]=Program05a(volt)
fruit_for = [];
for X=1:length(volt)
    if volt(X)>=31 && volt(X)<=40
        fruit_for= [fruit_for 'O']
    elseif volt(X)>=21 && volt(X)<=30
        fruit_for=[fruit_for 'G']
    elseif volt(X)>=11 && volt(X)<=20
        fruit_for=[fruit_for 'P' ]
    elseif volt(X)>=0 && volt(X)<=10
        fruit_for=[fruit_for 'A']
    elseif volt(X)<0 || 40<volt(X)
        fruit_for=[fruit_for 'U']
    end
end 

Answer 1

[Tyler Vincent]

I got it to work using the updated script shown above.

[Guillaume]

I would strongly recommed that you use (and understand) Andrei's solution instead of your own, which is very inefficient and very fragile.

In particular,

• you grow the fruit_for array in a loop. Your array should be preallocated otherwise, it's going to make your code very slow for even moderately large inputs.
• your code only works with a limited range of integers, but never check that the inputs are integer and within that range. It will return incorrect result with no warning that anything is wrong if that's no the case. There's probably nothing worse than code that appear to work but returns incorrect results.
• your code only works with vector inputs, will return a row vector even if the input is a column vector. If the input is a matrix, it will return partially incorrect results without otherwise informing the user.
• your solution is not scalable. What if you need 100 different threshold? How about 1000? Are you going to be typing 1000 elseif? Using discretize or histcounts as in Andrei's answer, you simply have to pass one array of thresholds.

[Tyler Vincent]

Hi Guillaume,

I had to use for loops with if statements for my class as it was a requirement of the assigment. I agree Andrei's work is much better and effcient than the method i'm using but for this class I had to do it in a manner like this. The range was a set amount of number's shown above for this assigment. Also i've done some revisions not shown in the script above.

Answer 2

[Andrei Bobrov]

volt=[18 33 31 34 15 37 10.5 48 50 38 35 39 42 33 31 1 5 9 13 11 27 35 -1 46 22 6 19 36];
ABS = sprintfc('%c','UAPGOU');

[~,~,ii] = histcounts(volt,[-inf,0:10:40,inf]);
fruit = ABS(ii);

or

fruit = discretize(volt,[-inf,0:10:40,inf], 'categorical', cellstr(('UAPGOU')'));

[Tyler Vincent]

Thanks for the help. This does get the output I want but I want to get that anwer using the for loop if statement. Is that even possible with my current configuration?

[Stephen23]

+1 very nice

Answer 3

[Walter Roberson]

if 31 <= volt(X) && volt(X) <= 40
    fruit = O;
elseif 21 <= volt(X) && volt(X) <= 30
    fruit = G;
and so on
end

However, you have not defined O, G, P, A, or U within the function. Also, if the input were 30.5 then is it really true that you would want U? And if the input were 44 is it really the case that you want the function to crash because fruit would not have been assigned to?

[Tyler Vincent]

Thanks for the input. I'm trying to get those variables "O,U,G,etc" to be created into a array. Like this [P O O O P O P U U O O O U O O A A A P P G O U U G A P O] from volt=[18 33 31 34 15 37 10.5 48 50 38 35 39 42 33 31 1 5 9 13 11 27 35 -1 46 22 6 19 36].

[Walter Roberson]

https://www.mathworks.com/help/comm/ug/quantization.html

[Tyler Vincent]

Thanks for trying to help me. I'm still confused on what is needed to acomplish this.

[Walter Roberson]

That function is from the Communications Systems Toolbox.

Use quantize() with the list of edges, and get back the corresponding index number. You can then use that to look up the table of corresponding characters. Or you could use categoricals to represent the values.

[Tyler Vincent]

Thanks for the idea. I took a different approach as shown above to get it to work.